commit-reach(repo_get_merge_bases_many_dirty): pass on errors

(Actually, this commit is only about passing on "missing commits"
errors, but adding that to the commit's title would have made it too
long.)

The `merge_bases_many()` function was just taught to indicate parsing
errors, and now the `repo_get_merge_bases_many_dirty()` function is
aware of that, too.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/merge-base.c

@@ -10,10 +10,13 @@
 
 static int show_merge_base(struct commit **rev, int rev_nr, int show_all)
 {
-	struct commit_list *result, *r;
+	struct commit_list *result = NULL, *r;
 
-	result = repo_get_merge_bases_many_dirty(the_repository, rev[0],
-						 rev_nr - 1, rev + 1);
+	if (repo_get_merge_bases_many_dirty(the_repository, rev[0],
+					    rev_nr - 1, rev + 1, &result) < 0) {
+		free_commit_list(result);
+		return -1;
+	}
 
 	if (!result)
 		return 1;

commit-reach.c

@@ -470,17 +470,13 @@ int repo_get_merge_bases_many(struct repository *r,
 	return get_merge_bases_many_0(r, one, n, twos, 1, result);
 }
 
-struct commit_list *repo_get_merge_bases_many_dirty(struct repository *r,
+int repo_get_merge_bases_many_dirty(struct repository *r,
 				    struct commit *one,
 				    int n,
-						    struct commit **twos)
+				    struct commit **twos,
+				    struct commit_list **result)
 {
-	struct commit_list *result = NULL;
-	if (get_merge_bases_many_0(r, one, n, twos, 0, &result) < 0) {
-		free_commit_list(result);
-		return NULL;
-	}
-	return result;
+	return get_merge_bases_many_0(r, one, n, twos, 0, result);
 }
 
 int repo_get_merge_bases(struct repository *r,

commit-reach.h

@@ -18,9 +18,10 @@ int repo_get_merge_bases_many(struct repository *r,
 			      struct commit **twos,
 			      struct commit_list **result);
 /* To be used only when object flags after this call no longer matter */
-struct commit_list *repo_get_merge_bases_many_dirty(struct repository *r,
+int repo_get_merge_bases_many_dirty(struct repository *r,
 				    struct commit *one, int n,
-						    struct commit **twos);
+				    struct commit **twos,
+				    struct commit_list **result);
 
 int get_octopus_merge_bases(struct commit_list *in, struct commit_list **result);